Field of Invention
The invention relates to a method for monitoring the operation of a wind energy plant comprising a tower, a nacelle arranged on the tower and a rotor, which has at least one blade angle adjustable rotor blade, wherein rotor blade vibrations of the at least one rotor blade are registered during the operation of the wind energy plant by means of at least one measuring device and at least one current natural frequency of the at least one rotor blade is established from the registered rotor blade vibrations, wherein at least one environmental parameter and/or at least one operational parameter is or are additionally registered, which parameter or parameters influences or influence the natural frequency of the at least one rotor blade. The invention furthermore relates to an operational control apparatus of a wind energy plant and a corresponding wind energy plant. The present invention relates in particular to monitoring the state of rotor blades of a wind energy plant.
Brief Description of Related Art
The rotor blades are amongst the components of a wind energy plant under the highest amount of strain during the operation thereof. The rotor blades are exposed to the wind and transfer the energy stored in the wind into a rotational movement, while being exposed to large shearing forces, bending forces, centrifugal forces, turbulence, changes of load, etc. Additionally, the rotor blades are also exposed to environmental influences such as solar radiation, rain, snow and ice accretion.
Although the rotor blades should be designed for high service life, they should also be as light as possible so as to operate a wind energy plant economically. In the design thereof, the aerodynamics, the occurring loads, the dynamics of operation, the possibility of closed-loop control and management, as well as the material should be taken into account. Here, inter alia, safety aspects include imbalances, resonances, dropping ice and material fatigue, which can likewise occur in rotor blades. In view of the efficiency, it is particularly the energy production related to the site and, accompanying this, wind measurements as well as the highest possible service life of the rotor blades that should be taken into account for the rotor blades.
Since the rotor blades may not be dimensioned too thick for reasons of efficiency, it is desirable to monitor the rotor blades during operation in order to ensure that measures can be adopted for reducing loads in the case of increased loads which go beyond the loads underlying the design of the rotor blades. An example for this lies in the use of the monitoring for identifying ice accretion on the rotor blades; this is desirable at many sites with a relatively cold climate. Ice accretion may already form at temperatures below 3° C. and, firstly, as additional mass, puts a strain on the rotor blades and, secondly, as a source for ice droppings, is a danger to humans, animals and objects over a large area.
A method and device for monitoring the state of rotor blades on wind power plants is known from DE 10 2005 017 054 A1. There, the state of rotor blades is monitored by way of measuring body-borne sound of at least one rotor blade using at least one sensor fastened to the rotor blade, which sensor is connected to a unit for wireless transmission of the output signals of the sensors to an evaluation unit, where a frequency spectrum is established from the signals by means of suitable methods, the frequency spectrum is compared to reference spectra which are stored in the evaluation unit, correspond to defined damage and extraordinary states and are parameterized, and the state of the rotor blade is established therefrom. Here, a body-borne sound measurement is brought about from a sequence of a plurality of individual measurements carried out immediately in succession, wherein the start of each one of these individual measurements is triggered by a uniform rotational angle of the rotor blade in relation to the rotational axis of the rotor, and all established frequency spectra of each individual measurement are accumulated prior to the comparison with the reference spectra.
By triggering by the uniform rotational angle, it is possible to establish not only the amplitude profile of the frequency spectrum but also the phase angle thereof. The measurements are performed with a high repetition rate or sampling rate in order to capture the harmonic spectrum. The amplitudes and phases of the individual harmonics of the fundamental waves (natural frequencies) of the rotor blade are converted into a vector which is then compared by means of suitable statistical methods to vectors of the frequency spectra for various damage cases in order to determine the similarity with known damage cases. Since this method is employable in a versatile fashion and very powerful, it requires an additional system which must be introduced into a wind energy plant.
By contrast, the present invention is based on the object of providing monitoring of the operation of a wind energy plant, in particular in relation to ice accretion or other damage cases, which ensures a reliable operation of the wind energy plant with little outlay.